Added support for nested accordions

Now it's possible to create child and parent accordions. To do this, just create another accordion inside of an existing accordion section and so on. Example(_See section 3 for the child accordion!_):

**HTML:**
```html
<!-- Accordion begin -->
<ul class="accordion_example">

	<!-- Section 1 -->
	<li>
		<div>Section 1. Just text</div><!-- Head -->
		<div>Content</div>
	</li>

	<!-- Section 2 -->
	<li>
		<div>Section 2. Just text</div><!-- Head -->
		<div>Content</div>
	</li>

	<!-- Section 3 -->
	<li>
		<div>Section 3. This has a child.</div><!-- Head -->
		<div>

			<!-- Another Accordion here -->
			<ul class="accordion_example">
				<!-- Section 1 -->
				<li>
					<div>Section 1</div><!-- Head -->
					<div>Quick text</div><!-- Content -->
				</li>

				<!-- Section 2 -->
				<li>
					<div>Section 2</div><!-- Head -->
					<div>Quick text</div><!-- Content -->
				</li>
			</ul>
			<!-- Another Accordion here end -->

		</div>
	</li>

</ul>
<!-- Accordion end -->
```
**JS:**
```js
$(".accordion_example").smk_Accordion();
```

**The demo code is available in index2.html.**